Abstract
There are many typical symmetric large plastic deformation problems in aluminum alloy stamping. Warm stamping technology can improve the formability of materials and obtain parts with high-dimensional accuracy. Friction behavior in the stamping process is significant for the forming quality. An accurate friction coefficient is helpful in improving the prediction accuracy of forming defects. It is hard to obtain a unified and precise friction model through simple experiments due to the complicated contact conditions. To explore the effect of friction behavior on the forming quality, warm friction experiments of the AA6061 aluminum alloy and P20 steel with different process parameters were carried out using a high-temperature friction tester CFT-I (Equipment Type), including temperatures, the interface load, and sliding speeds. The variation curves of the friction coefficient with various parameters were obtained and analyzed. The results show that the friction coefficient increases with temperature and decreases with the sliding speed and load. Then, the influences of process parameters on the surface morphology of the samples after friction were observed by an optical microscope; adhesive wear occurred when the temperature increased, and the surface scratch increased and deepened with the increase in the load. Finally, the friction coefficient models of the speed and load were established by analyzing the data with Original software. Compared with the experimental and the finite element analysis results of the symmetrical part, the errors of the velocity friction model in thickness and springback angle are less than 4% and 5%, respectively. The mistakes of the load friction model are less than 6% and 7%, respectively. The accuracy of the two friction models is higher than that of the constant friction coefficient. Therefore, those coefficient models can effectively improve the simulation accuracy of finite element software.
Highlights
At present, lightweight technology can effectively improve fuel efficiency and has become the trend of the development of the automobile industry [1]
The Coulomb friction law or constant friction factor model is widely used in sheet metal forming numerical simulation software, and the friction factor is often input as a regular [7], which results in a deviation between the actual value and the numerical simulation results
The friction properties of the AA6061 aluminum alloy and P20 steel were tested by the CFT-I friction tester under different temperatures, sliding speed, and normal load
Summary
Lightweight technology can effectively improve fuel efficiency and has become the trend of the development of the automobile industry [1]. There are many typical symmetric plastic deformation problems in the aluminum alloy forming process. These include drawing cylindrical parts, rounding holes, flanging circular plates, necking, expanding, bulging, etc. Warm stamping is a new process that can effectively enhance the deep drawing formability of aluminum alloy, increase the strength of materials, reduce the internal stress, reduce the springback, and significantly improve the surface quality and forming accuracy [5]. The warm stamping of aluminum alloys is a complicated thermal-mechanical coupling process, and friction behavior is the critical factor influencing the forming quality and die life [6]. The friction behavior of the stamping process is quite complex, including the changing interaction variables in the forming process, deformation, forming speed, materials, surface roughness, tool geometry, etc. To improve the accuracy of numerical simulation results, it is necessary to profoundly and systematically study the friction and contact problems in the forming process of aluminum alloy sheets and obtain the accurate friction factor of the aluminum alloy under different process conditions
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